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1.
The addition of molybdenum (0.05 mmol kg-1 dry-matter) to the diet of lambs given a trickle infection of Haemonchus contortus larvae (500 third stage larvae d-1 over six weeks) reduced mean faecal egg counts (epg) from 3952 to 2312 +/- 402 by 32 days (P less than 0.02) and greatly reduced the mean number of worms recovered from the abomasum 14 days after infection ceased (907 compared with 4167: P less than 0.01). Infection reduced haemoglobin concentrations less in lambs given molybdenum although the difference was small relative to the reduction in worm burden. Lambs not given molybdenum had low intraepithelial mast cell counts in the abomasal mucosa and less abomasal hypertrophy than expected from abomasal parasitism. Molybdenum did not consistently reduce the copper status of the host or the parasite. Previous exposure to molybdenum greatly reduced protein but not proteinase activity in, or secreted by, adult worms cultured for eight hours. It is suggested that molybdenum either increased the inflammatory response which preceded worm rejection or that it indirectly enhanced that reaction by reducing the effectiveness of copper-dependent, anti-inflammatory enzymes in the gastrointestinal mucosa.  相似文献   

2.
Anthelmintic trails, conducted with albendazole, fenbendazole and ivermectin for efficacy against gastrointestinal nematodes, principally inhibited early fourth larval stages of Ostertagia ostertagi in naturally infected cattle. Cattle wee slaughtered seven to 20 days after treatment. O ostertagi was the predominant abomasal nematode recovered with occasional small numbers of Haemonchus species and Trichostrongylus axei. Control calves uniformly had very large O ostertagi infections, primarily early fourth stage larvae. Viable surviving worms and variable numbers of dead and degenerate worms were recovered in abomasal contents and washings. These O ostertagi larvae and adults were characterised by adherent debris or proteinaceous material, degenerated cuticles and distortion of internal structures. This study demonstrated the necessity for proper timing of slaughter for anthelmintic trial evaluation to allow clearance of dead nematodes, specifically O ostertagi larvae which are sequestered in the abomasal glandular tissue. Nematode collection within seven to 12 days after treatment will include dead and degenerate larval nematodes. The peripheral coating of larvae was suggestive of the Splendore-Hoeppli effect which has been associated with immunological responsiveness. The antigenic stimulus for this material and the lymphocyte and eosinophil infiltration was suspected to be early fourth stage O ostertagi larvae within the mucosa but was not identified definitively.  相似文献   

3.
Previous studies have indicated that host genetics significantly affects the number of gastrointestinal nematode eggs per gram (epg) in the feces of calves during their first grazing season. An entire calf crop of approximately 190 animals was monitored monthly until weaning to verify these earlier results, and to begin to discern the basis for this phenomenon. A significant genetic effect on fecal epg values was not observed until calves had been on pasture for 2-3 months, and was demonstrable until late in the grazing season when the effect was lost. The loss of a genetic effect coincided with the appearance of significant numbers of the more highly fecund nematode species Haemonchus placei and Oesophagostomum radiatum, and with an apparent increase in Ostertagia ostertagi transmission, indicating that the observed genetic control of epg values may be species specific, dose dependent or both. Calves were selected from the population, and grouped according to their epg phenotype over the grazing season as either high or low epg calves. Postmortem examination of some of these calves indicated that worm burdens in the low epg calves were 60% of those of the high epg calves. Experimental challenge inoculation of the remaining calves indicated that: (1) challenge with Cooperia oncophora resulted in low epg calves harboring worm numbers that were 65% of those of high epg calves; (2) challenge with O. ostertagi resulted in similar numbers of worms in both groups, but the fecundity of worms in the low epg groups was significantly lower (P less than 0.05) than in the high epg group. Analysis of serum anti-Ostertagia antibody levels in the grazing calf population showed rises in serum IgG1, IgG2, IgM and IgA antibody levels during the grazing season. Peak serum IgG2 and IgG1 anti-Ostertagia antibody levels were found to be significantly affected by host genetic factors while IgA and IgM levels were not under such control.  相似文献   

4.
The efficacy of febantel at a dosage of 5 mg/kg (45.5% paste formulation) against inhibited early 4th-stage larvae (EL4) of Ostertagia ostertagi, other nematodes of the abomasum, and Dictyocaulus viviparus was investigated in 4- to 6-month-old Holstein calves that grazed on pasture heavily contaminated with parasites from February 24 to April 1, 1986 (36 days). In Louisiana, this is the first month of a 3-month period in which increasing numbers of inhibition-prone O ostertagi larvae are acquired, and infection risk with D viviparus may remain high. Three of 4 calves that died of lungworm infection during the pasture-exposure period were necropsied. Large numbers of abomasal nematodes, including inhibited O ostertagi larvae, and large numbers of D viviparus were recovered. Twenty-five calves were randomly allotted by equal distribution of body weight to 2 groups and treated on April 4: placebo-treated calves (n = 13) and febantel-treated calves (n = 12). Equal numbers of treated and control calves were killed at 6 and 7 days, respectively, after treatment. Mean numbers of O ostertagi in control cattle were: adults, 4,931; developing 4th-stage larvae (DL4), 1,119; and inhibited EL4, 3,410. Ostertagia lyrata, Trichostrongylus axei, Haemonchus sp, and D viviparus were well distributed in nearly all control calves. Percentage reduction of O ostertagi in treated calves, when compared with controls, was: adults, 83.6%; DL4, 57.8%; and inhibited EL4, 34.8%. Percentage reductions of other species were: O lyrata, 92.6%; T axei adults, 99.3% and 4th-stage larvae (L4), 100%; Haemonchus sp adults, 66.7%, and L4, 64%; D viviparus adults 90.6%, and immature forms, 97.1%.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

5.
The efficacy of netobimin (Coded SCH 32481, Schering Corporation) in removing naturally acquired gastrointestinal nematode infections was evaluated in 10 treated and 10 untreated (control) yearling beef heifers. The anthelmintic was administered as an oral drench at a dose level of 7.5 mg kg-1 body weight. Fecal egg per gram (EPG) counts were reduced with netobimin by 98% (P less than or equal to 0.01) at both 1 and 2 weeks post-treatment (PT). The compound was highly effective in removing Oesophagostomum radiatum (100% at P less than or equal to 0.01), Cooperia spp. (97.66% at P less than or equal to 0.01) and Nematodirus helvetianus (100%, although not significant), but was ineffective against immature Ostertagia ostertagi (3.19%) and only moderately effective against adult forms (66.14% at P less than or equal to 0.05). The low efficacy against adult O. ostertagi was partially attributed to the maturation of fourth-stage larvae, not removed by the 7.5 mg kg-1 treatment, during the 14-day treatment-slaughter interval. Efficacy against Trichuris spp. could not be evaluated due to low levels and unequal numbers of worms recovered in the groups. The overall efficacy against adult species, excluding Trichuris spp., was 67.40% (P less than or equal to 0.05). No adverse reactions or signs of toxicosis were observed in heifers treated with netobimin.  相似文献   

6.
The efficacy of the morantel sustained release bolus (MSRB) in reducing gastrointestinal parasitism in first season grazing calves was evaluated during the summer--autumn grazing seasons of 1982 and 1983 in western Oregon. Each of 38 calves (1982) and 40 calves (1983) were randomly assigned to either control or treatment groups which were given MSRB on the day of turnout onto pasture. Mean worm burdens from tracer calves grazed with treated animals in 1982 and 1983 showed overall reductions of 86.4% (P greater than 0.05) and 84.3% (P less than 0.01), respectively, compared to tracers grazed with controls. Ostertagia ostertagi, Cooperia oncophora and Nematodirus helvetianus were the primary nematodes collected at necropsy. Twelve full-season 1982 tracer animals (6 treated and 6 control) indicated an 88.1% (P less than 0.05) overall reduction in mean worm burdens. Mean fecal worm egg per gram (EPG) counts of treated animals reflected a reduction of 69% (P less than 0.05) in 1982 and 90% (P less than 0.05) in 1983. Autumn inhibition of O. ostertagi was observed. In the 1982 trial the control animals showed a slight mean weight gain advantage over the treated group from Day 84 until Day 160 (trial termination) when the mean difference was 7.9 kg. The final mean weight gain advantage of treated animals in 1983 was 13.5 kg (P less than 0.05). These trials demonstrated that the MSRB was an effective anthelmintic for reducing gastrointestinal parasitism in grazing calves and for decreasing pasture larval contamination.  相似文献   

7.
Three groups of 11 naturally infected crossbred beef calves were injected subcutaneously with moxidectin 1 per cent injectable at 0.2 or 0.3 mg moxidectin/kg bodyweight or with the unmedicated vehicle. Nematode infections had been acquired during grazing from December to April. Based on the faecal egg counts and total worm counts of the control calves at necropsy (11 to 13 days after treatment) most of the calves had heavy parasitic burdens. Ostertagia ostertagi was predominant and the mean numbers of adults, developing fourth stage larvae (L4) and inhibited early L4 were 45,906, 10,061 and 68,918, respectively. Haemonchus placei and Trichostrongylus axei were also present in the abomasa. Three species of Cooperia, Oesophagostomum radiatum L4 and T colubriformis adults were found in the intestinal tract. Both dosages of moxidectin were equally effective (P < 0.05) against all the abomasal nematodes (99.9 to 100 per cent) and the intestinal tract nematodes (99.4 to 100 per cent). No adverse reactions to the moxidectin treatment were observed. Abomasal pathology characteristic of heavy O ostertagi infection was observed in the control calves, but not in the treated calves.  相似文献   

8.
Levamisole (LEV) was tested in four experiments to compare efficacy values against Ostertagia ostertagi when larval maturation was occurring (September), following inhibition and also when populations were expected to be largely adult (winter). A primary objective was to determine the importance of developing fourth-stage larvae (DL4) and inhibited, early fourth-stage larvae (EL4) in replacing adult worms lost through treatment and the effect of this on reduced efficacy against adult worms. Young crossbred beef calves ranging in weight from 150 to 230 kg were used in the first (September 1981), second (September 1983) and third experiments (January 1987). Jersey calves of 110 kg average weight were used in the fourth experiment (December 1988). Calves were randomized to groups according to weight and group sizes ranged from three to five calves. All parasite infections were naturally acquired, but a mixture of nematode third-stage larvae (L3) (22,500 per calf), including 20% Ostertagia ostertagi, was inoculated into Jersey calves of Experiment 4 following a 2 week exposure to natural infection. All LEV treatments were by subcutaneous injection at dosages of 6 and 8 mg kg-1. Treatment with ivermectin was used only in Experiment 3 as an efficacy reference. All calves were killed at 8-10 days after treatment. The efficacy of LEV against all developmental stages of Ostertagia ostertagi was consistently low in all experiments and a dose-dependent response was not evident. Large numbers of all Ostertagia ostertagi developmental stages were present in non-treated calves in both September experiments. Percent reduction of adults, DL4 and EL4 at the 6 mg kg-1 and 8 mg kg-1 dosages, respectively, were adults, 51.7 and 23.6 (1981), 8.7 and 51.3 (1983); DL4 40.3 and 13.2 (1981), 37.9 and 33.1 (1983); EL4, 19.6 and 0 (1981), 59.6 and 42.9 (1983). Smaller numbers of Ostertagia ostertagi were present in winter experiments and adult worms greatly outnumbered larval stages. Percent reductions of adults, DL4 and EL4, respectively, were (1987) LEV 6 mg kg-1, 40.2, 0 and 0; ivermectin 200 micrograms kg-1, 98.7, 97.7 and 100.0; (1988) LEV 6 mg kg-1, 62.4, 100.0 and 100.0; LEV 8 mg kg-1, 49.1 65.0 and 74.1. Too few larval stages were present in the latter experiment for valid efficacy values.(ABSTRACT TRUNCATED AT 400 WORDS)  相似文献   

9.
The anthelmintic efficacy of abamectin (avermectin B1) was evaluated against gastrointestinal nematodes, including Ostertagia ostertagi inhibited larvae and lungworm, in yearling crossbred beef heifers during late spring. The calves were grazed on contaminated pasture for 10 weeks and then held under conditions free of nematode infection for 3 weeks prior to allotment and treatment on 5 June. Thirteen calves were randomly assigned to two groups of six by restricted randomization on body weights; the extra lightest calf was assigned to the non-treated control group. Group 1 calves were treated with abamectin at 200 micrograms kg-1 body weight by s.c. injection and Group 2 calves were not treated; all were killed at 14 days after treatment. Ostertagia ostertagi was present in all controls; arithmetic mean numbers of adults, developing fourth stage larvae (L4) and inhibited EL4 were 7683, 605 and 36,102, respectively. Other nematode genera present in controls in sufficient numbers for the experiment were Haemonchus placei adults, Trichostrongylus axei adults, Cooperia spp. adults, Oesophagostomum radiatum adults, Bunostomum phlebotomum adults, Dictyocaulus viviparus adults and E5 (immature adults). Abamectin was highly effective (consistently greater than 99% efficacy and P less than 0.05) in removing all nematodes present in treated calves as represented in non-treated controls, including the primary target of Ostertagia ostertagi inhibited EL4. The lowest efficacy was 93.8%, against D. viviparus E5.  相似文献   

10.
Parasite-free 4-month-old calves were inoculated with Ostertagia ostertagi and/or Trichostrongylus axei followed 6 weeks later by increasing doses of O ostertagi for 8 weeks. Clinical signs of parasitism, fecal egg counts, and plasma pepsinogen concentrations were monitored, and gross lesions and parasite burdens were determined postmortem. Clinical signs of parasitism were not observed and weight gains were not affected in experimentally infected calves. In calves infected with O ostertagi, mean plasma pepsinogen concentrations were greater than for control calves and were diagnostically significant 4 weeks after inoculation and during the last 4 weeks of serial inoculations with O ostertagi. In calves that were given O ostertagi and T axei, abomasal pH was significantly increased, and abomasal lesions were more pronounced than in control calves or in calves inoculated with only O ostertagi or T axei. Abomasal lymph nodes were enlarged in all parasitized calves; other lymph nodes in the calves inoculated with both O ostertagi and T axei were usually smaller than in calves inoculated with only O ostertagi or T axei. Numbers of O ostertagi-inhibited larvae were small in all inoculated calves, but the percentage inhibition was significantly greater in calves inoculated with both O ostertagi and T axei. The percentage inhibition was 3.53% for the O ostertagi-inoculated calves and 7.07% for calves inoculated with both O ostertagi and T axei. These percentages indicated a synergistic effect of concurrent abomasal parasitism, whereas a synergistic effect on T axei worm burden was not observed. The low percentage of larval inhibition indicated that factors other than host resistance are involved in naturally occurring pretype II ostertagiosis.  相似文献   

11.
Various single or multiple doses of Ostertagia ostertagi were administered to young calves, and the production of protection phenomena elicited by single challenge inoculations ranging from 50,000 to 300,000 larvae or multiple challenge inoculations totaling 98,000 and 300,000 larvae was investigated. With some regimens, the vaccinations apparently resulted in protection against challenge exposure, as reflected by 36 to 56% fewer worms becoming established in challenge-exposed vaccinated calves than in challenge-exposed nonvaccinated, control calves. Other protection phenomena were elicited by some vaccinated calves of significantly more female worms lacking the distinctive vulval flap of O ostertagi and harboring significantly fewer eggs per female. Challenge exposure with a pathogenetic dose of 300,000 larvae produced the same degree of retarded weight gain in vaccinated as in nonvaccinated calves, and at necropsy, visceral lesions and pathologic alterations were equally severe in both groups of calves.  相似文献   

12.
Friesian calves given a low level infection of the abomasal parasite Ostertagia ostertagi over a six week period displayed a mild diarrhoea with high faecal egg counts and elevated plasma pepsinogen values. At necropsy on day 23 abomasal lesions characteristic of ostertagiasis were widespread. At 42 and 84 days oedema and congestion were also prominent. Total worm burdens on days 23 and 42 were similar but a marked decrease had occurred by day 84. Feed digestibility and nitrogen economy were not markedly affected but radioisotopic measurements demonstrated an increase in albumin disappearance and catabolic rates, and plasma faecal clearance during the course of the infection. Prior administration of a morantel sustained release bolus to a group of similarly infected calves reduced the total worm burdens to less than 50 per cent of those recorded in the infected calves on days 23 and 42 and this fell to 3 per cent on day 84. Abomasal damage and the adverse pathophysiological changes associated with infection were prevented in this group.  相似文献   

13.
The efficacy of ivermectin against inhibited early 4th-stage larvae of ostertagia ostertagi and other nematodes of the abomasum and intestinal tract was determined in naturally infected yearling beef cattle. The time when large numbers of inhibited larvae were acquired was determined by monthly slaughter of monitor cattle, beginning in January. In April, 12 animals were removed from pasture and maintained free of further helminth exposure until slaughter (21 days). At 9 days after the cattle were removed from pasture, ivermectin was administered to the principals by subcutaneous injection (200 micrograms/kg); the other 6 animals were given subcutaneous injections of the ivermectin vehicle. both groups were klled and necropsied at 12 days after treatment. Mean numbers of O ostertagi in the 6 controls were: adults, 41,906; developing 4th stage, 73,813; and early 4th stage, 334,965. The mean proportion of early 4th-stage larvae was 73.7%. In the 6 principals (treated with ivermectin), the following reductions were observed: O ostertagi adults, 100%; developing 4th stage, 99.8%; and early 4th stage, 99,9%. Small numbers of dead and degenerated O ostertagi of all developmental stages were recovered from abomasal washings before fixation; few viable worms were recovered.  相似文献   

14.
The relationship between egg elimination and parasitic burden was studied in two groups of 12 lambs experimentally infected with 1000 and 3000 Dicrocoelium dendriticum metacercariae, respectively. Half the animals in each group were slaughtered 2 months post-infection (p.i.) and the other half 6 months p.i. In order to detect and follow elimination of D. dendriticum eggs by the lambs, faeces samples collection started one and a half months p.i. and continued fortnightly until the end of the experiment. Egg elimination was first detected between days 49 and 79 p.i. (mean = 59 +/- 1.6 SE). Mean eggs per gram (epg) was higher in the lambs infected with 3000 metacercariae (347.2 +/- 42.4 epg) than in those infected with 1000 (194.8 +/- 14.4), although no significant differences were detected between both groups using the Student 't' test. Egg elimination was higher in the faeces samples taken in the afternoon (mean = 357.8 +/- 47.6 epg) than in those from the morning (mean = 215.7 +/- 21.3). The percentage of metacercariae which became established as worms was higher in the animals dosed with 1000 metacercariae (21.6%) than in those infected with 3000 (16.3%). The number of worms recovered on necropsy of each animal varied between 30 and 2063 (mean = 346.6 +/- 80.5) and their length between 2.6 and 7.1 mm (mean = 5.2 +/- 0.1). The mean number of parasites for lambs infected with 3000 metacercariae (489.3 +/- 163.1) was higher than that obtained from those dosed with 1000 (215.7 +/- 41.4), although more worms were collected in some cases from the lambs infected with the latter dose than the former. In general there was an increase in the number of epg eliminated as days p.i. and parasitic burden increased. A positive relationship was observed via the correlation coefficient between the number of epg eliminated by each of the lambs throughout the experiment and that of worms recovered. This relationship was more intense on considering only the number of epg eliminated between days 120 and 180 p.i.  相似文献   

15.
Summary The activity of albendazole against gastrointestinal helminths in naturally infected calves in the Netherlands was tested. The calves were in their fist grazing season and kept in two groups of ten. One of these groups was grazed alternately with sheep. Five out of each group were drenched with albendazole (7.5 mg/kg) on the day they were housed (November 1). Before and 2, 14, and 28 days after treatment individual faecal samples were taken from all calves and larval cultures were made. Ten calves, six treated and four untreated, were killed for post mortem studies 14 days after treatment The remaining calves were slaughtered 14 days later. The drug was highly effective in reducing the egg output, measured as the number of larvae cultured per gram of faeces. Compared with the untreated calves, the reduction was more than 99% two days after treatment, 100% at 14 days, and 99% after 28 days. It was shown that egg output 28 days after treatment came from worms which had developed from arrested larvae of Ostertagia ostertagi that had survived treatment. Post mortem results showed an efficacy of 100% against adult O. ostertagi, of almost 100% against Trichostrongylus axei, and 100% against adult and larval Cooperia oncophora. Twenty-eight days after treatment, the reduction of arrested early fourth stages of O. ostertagi was 85% in comparison with the untreated calves. Apparently less effect was found against Trichuris ovis at the given dose rate.  相似文献   

16.
Twelve dairy calves, naturally infected with lungworms and gastrointestinal parasites, were selected for a controlled test with single doses of ivermectin, administered subcutaneously, at the dose rate of 200 micrograms/kg. Specific interest was on efficacy of ivermectin against lungworms (Dictyocaulus viviparus), with ancillary interest directed on abomasal parasites. Ivermectin was administered to 6 calves, and the vehicle only, to 6 calves. At necropsy, 7 days after treatment, lungworms were not recovered from any of the treated calves; nontreated calves, given the vehicle only, were infected with 1 to 46 lungworms each. Removal efficacy against adult Ostertagia ostertagi was 99%. Fourth-stage Ostertagia spp and Trichostrongylus spp and mature Trichostrongylus axei, present in low numbers, were all removed. The fecal egg count for gastrointestinal parasites indicated all eggs, except for a few Nematodirus eggs, were cleared from treated calves. One treated calf showed signs of irritation of the neck at injection site for a short time after treatment and 1 treated calf had a slight indurated area at injection site at necropsy.  相似文献   

17.
The efficacy of the morantel sustained release bolus (MSRB) in controlling gastrointestinal parasitism in beef cattle was assessed during the 1982 spring-autumn grazing season. Forty-eight cows and their calves were allotted to three equal groups. One group (T-1) served as a nonmedicated control group. One MSRB was administered to each calf of the T-2 group, and to each cow and calf of the T-3 group at the beginning of the study. The efficacy of the bolus was assessed by comparison of weight gain performance and parasitological data (fecal worm egg counts, herbage larval counts, worm counts from tracer and principal trial calves, and plasma pepsinogen level determinations). Though not statistically significant, treated calves from Group T-2 had a numerical mean weight gain advantage of 2.6 kg, and those from Group T-3 of 4.7 kg, over control calves. Average daily gains (ADG) for the three groups of calves were 0.69, 0.72, and 0.73 kg, respectively. Untreated cows from Group T-2 and treated cows from Group T-3 outperformed the control cows by 12.3 and 7.5 kg, respectively. Fecal worm egg counts from both groups of treated calves were significantly (P less than 0.01) lower than counts from control calves during the entire 169-day trial; notably, egg counts were reduced by 99% 28 days after MSRB administration to both groups of calves. There were no significant differences in the number of eggs counted from the three groups of cows, probably because of the very low numbers of eggs encountered. Mean total worm burdens of principal calves (six per group) necropsied at trial termination indicated a 91% (P less than 0.01) reduction in Group T-2 and an 87% reduction (P less than 0.01) in Group T-3. Worm-free tracer calves were introduced onto pastures every 28 days to monitor availability of infective larvae. The mean number of worms recovered at necropsy from tracer calves that grazed with control cattle increased as the season progressed. However, the numbers of parasites recovered each month from mid-August through mid-October from tracers that grazed pastures with treated cattle were lower (P less than 0.05) than those levels displayed at trial initiation. In addition, the mean numbers of worms from treated group tracers were lower than from the controls for each necropsy period.(ABSTRACT TRUNCATED AT 400 WORDS)  相似文献   

18.
Two controlled tests were conducted in 1981 and 1982 in dairy calves on the University of Kentucky research farm to determine activity of the bolus formulation of levamisole given at the dose rate of 8 mg/kg against naturally occurring infections of Ostertagia ostertagi. Removal efficacies of mature O ostertagi were 98% in the 1981 test (3 treated and 3 nontreated calves) and 94% in the 1982 test (7 treated and 8 nontreated calves). Against immature Ostertagia spp, removal efficacies were 100% and 65% for the 1st and 2nd tests, respectively. The calves were grazed on the same pasture as dairy calves in previous controlled tests in 1979 and 1980 where activity of levamisole against mature O ostertagi (data recently published) was much less than in the present tests. It does not appear that the poor performance in the early tests can be attributed to the drug resistance phenomenon. Data on overwinter survival (119 days) of free-living stages of gastrointestinal parasites on pasture were derived from the nontreated calves in the 1982 controlled test. The calves, raised helminth-free, were placed on the pasture on Apr 5, 1982. Helminths recovered at necropsy of the calves, besides O ostertagi, included Trichostrongylus axei, Nematodirus helvetianus, Nematodirus spp, Cooperia oncophora, Trichuris spp, and Moniezia spp. The lung-worm, Dictyocaulus viviparus, previously found in cattle on the farm, was not found in these calves.  相似文献   

19.
A 168-day study was conducted to evaluate the effect of a strategically timed treatment with fenbendazole on anthelmintic efficacy and performance of beef cows and calves. Eight groups of 10 Angus cow/calf pairs were allotted on 7 May 1987 to eight similarly managed 4.86-ha pastures (bermudagrass/tall fescue) on the basis of cow age, and calf sex and weight. At that time, four groups of cows received a dose of fenbendazole (5 mg kg-1) with their calves receiving fenbendazole at the same dosage 28 days later. Treated calf average daily gain (ADG) was 0.04 kg greater (P less than 0.05) than control calves (0.82 vs. 0.78 kg) during the 168-day study. Treated cow ADG was 0.09 kg greater (P less than 0.05) than control cows (0.40 vs. 0.31 kg). Although there was a reduction (P less than 0.05) in fecal egg counts following treatment of the cows, the numbers of eggs generally were low compared with egg counts of calves. From Day 28 through Day 112 post-treatment, fecal egg counts of treated calves were lower (P less than 0.05) than those of control calves. However, fecal egg counts from treated calves increased post-treatment until there were no differences (P greater than 0.05) between treated and control calves at the end of the study. The pregnancy rate tended to be higher (P = 0.12) for treated cows (98%) than for untreated control cows (75%). The actual calving rate was higher (P = 0.03), for treated cows (90%) than for untreated control cows (68%). Results indicated that a strategic anthelmintic treatment can improve cow and calf performance, but that calves born in late winter or early spring may need more than one therapeutic dose during the nursing period on pasture.  相似文献   

20.
Four groups of 18 beef calves each were used to evaluate effects of different treatments on parasite control and weight gains. The investigation extended from November 1986 (weaning) to October 1987. Group-1 calves were treated with ivermectin (200 micrograms/kg of body weight, SC) at approximately 6-week intervals for a total of 8 treatments; group-2 calves were given the same dosage of ivermectin by the same route of administration as group-1 calves in November, March, and July; group-3 calves were given fenbendazole paste (5 mg/kg, PO) at the same times as group-2 calves; and group-4 calves served as untreated controls with provision for ivermectin salvage treatment. All groups grazed on individual pairs of larval-contaminated, 1.6-ha pastures. Highest (P less than 0.05) initial worm counts in fall tracer calves were found in group 3 (Ostertagia ostertagi and Trichostrongylus axei adults) and group 4 (O ostertagi and Haemonchus adults). Fecal egg counts of group-1 calves were low throughout the experiment and pasture larval counts remained negligible after July. Egg counts and larval counts of other groups remained higher into summer. Worm counts, including O ostertagi inhibited early fourth-stage larvae (EL4), were highest (P less than 0.05) in groups-3 and -4 spring tracer calves; numbers of O ostertagi EL4 were similarly high in groups 2, 3, and 4; and T axei counts were highest (P less than 0.05) in groups-3 and -4 yearlings slaughtered in spring. Liveweights of group-1 calves were greater (P less than 0.05) than in other groups from March 2 to October, and by July 2, group-2 calves had a liveweight advantage over group-4 calves. Group-3 calves had the lowest rate of gain from March to July and mean liveweight of the group was less (P less than 0.05) than in all other groups from April to October. Only minimal worm numbers were recovered from groups-1 or -2 calves in October. Large numbers of O ostertagi and T axei were recovered from group-4 calves and O ostertagi from group-3 calves. A few calves in groups 3 and 4, but particularly in group 4, were affected by type-II disease (chronic to acute gastritis caused by maturation and emergence of previously inhibited larvae) from August to October. Final mean liveweights in descending order were 365 kg in group 1, 328 kg in group 2, 316 kg in group 4, and 281 kg in group 3.  相似文献   

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